Fuel Composition Derived from Biodiesel

ABSTRACT

The present invention relates to a fuel composition and method for the preparation thereof. The fuel composition is particularly useful as an aviation fuel and as a ground transportation fuel in cold weather environments. The fuel composition includes oil derived from a biological source such as vegetable oil and/or animal fat. Further, the fuel composition can be based on biodiesel. Moreover, the fuel composition of the present invention includes a reduced amount of oxygen as compared to the biodiesel or substantially no oxygen.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/227,583, filed Jul. 22, 2009, and entitled“Conversion and Purification of Biodiesel to Aviation Fuel.”

FIELD OF THE INVENTION

The present invention relates to a fuel composition and a method ofproducing the fuel composition. In particular, the fuel composition canbe useful in cold temperature environments and as aviation fuel.

BACKGROUND OF THE INVENTION

Global climate change is causing a shift in the sources of energy fromfossil fuels to more sustainable and renewable resources, such asbiodiesel. For ground transportation, there is a significant developmenteffort to use electricity from non-fossil primary fuel to power cars,trucks and rail systems. However, in cold climates, such as in temperateor polar regions of the world (including a significant portion of theUnited States, Canada, northern Europe and northern Asia), biodieselfuels tend to solidify rendering inoperable engines that use it.

Furthermore, for aircraft, the energy densities available frombatteries, fuel cells and other portable sources are not sufficient.Aviation fuel, such as jet fuel, is generally a specialized type ofpetroleum-based fuel used to power an aircraft and is generally of ahigher quality than fuel used for ground transportation. Aviation fuelis designed to remain liquid at cold temperatures as found in the upperatmosphere where aircraft fly. Aviation fuels can include hydrocarbons,such as paraffins; olefins; naphthenes and aromatics; antioxidants; andmetal deactivators. Known aviation fuels include jet fuels, such asJP-5, JP 8, Jet A, Jet A-1, and Jet B. Aviation requires a high energydense liquid fuel to achieve the speeds and distances airplanes candeliver today. Jet fuel has the highest volumetric energy density ofliquid fuels, such as ethanol, butanol, bio-kerosene, and biodiesel.

There is a need in the art to develop a fuel composition that does notsolidify in cold temperature environments for use as groundtransportation fuel, that satisfies the specified standard requirementsfor use as aviation fuel, and is based on sustainable and renewableresources, such as biodiesel.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a fuel compositionincluding oil derived from a biological source and alcohol. The fuelcomposition is at least substantially free of oxygen andoxygen-containing compounds.

The oil may be selected from the group of biological sources includingvegetable oil, crop seed oil, animal oil, animal fat, and combinationsthereof.

The alcohol may be selected from the group consisting of methanol,ethanol, propanol, isopropanol, butanol, and mixtures thereof.

The fuel composition may be oxygen free. In another embodiment, the fuelcomposition may have a level of oxygen that is less than the level ofoxygen in biodiesel. In yet another embodiment, the fuel composition mayhave a level of oxygen that is less than 2000 parts per million oxygenbased on the fuel composition.

The fuel composition includes molecules and each of the molecules mayhave a carbon chain length of from 12 to 14 carbon atoms.

The fuel composition may be used for aviation fuel. In anotherembodiment, the fuel composition may be used for ground transportationfuel in a cold climate.

The fuel composition may include an alkane.

The fuel composition may further include a catalyst. The catalyst may beselected from the group consisting of calcium hydroxide, potassiumhydroxide and mixtures thereof.

In another aspect, the present invention provides a method for preparinga fuel composition. The method includes reacting oil derived from abiological source and alcohol to produce an alkyl ester-containingproduct; and removing at least a portion of oxygen from the alkylester-containing product to produce a fuel composition which is at leastsubstantially free of oxygen and oxygen-containing compounds.

In an embodiment, the alkyl ester-containing product may include analkyl ester selected from the group consisting of methyl ester, ethylester, propyl ester, isopropyl ester, butyl ester and mixtures thereof.

In another embodiment, the alkyl ester-containing product may includebiodiesel.

In the method, the reacting step may be conducted in accordance with atransesterification reaction.

In the method, the removing step may be conducted in accordance with anucleophilic acyl reaction.

In an embodiment, the cloud point of the fuel composition may be lowerthan the cloud point of the alkyl ester-containing product.

In the method, the removing step may further include removing a portionof carbon atoms from the alkyl ester-containing product.

In the method, the fuel composition includes molecules and each of themolecules may have a carbon chain length of from 12 to 14 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention as set forth in the claims will become more apparent fromthe following detailed description of certain preferred practicesthereof illustrated, by way of example only, and the accompanyingdrawings, wherein

FIG. 1 is a schematic showing a reaction process for reducing an ethylester to ethanol in accordance with an embodiment of the presentinvention; and

FIG. 2 is a schematic showing a process for chemoselectively reducingsecondary and tertiary alcohols (e.g., 2-decanol) to alkanes (e.g.,decane) in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a fuel composition and method thereof.The fuel composition can be used in various applications. In particular,the fuel composition can be employed as a cold weather fuel for use inground transportation vehicles, such as trucks, automobiles, railroads,and the like, and as an aviation fuel for use in aircrafts, such asairplanes, helicopters, and the like. Further, the fuel composition ofthe present invention can be prepared based on biodiesel. For example,biodiesel can be produced and converted to a fuel composition that issuitable for use as cold weather ground transportation and aviationfuel. Biodiesel is derived from plant oils, algae oils, and animal fats,and therefore, the present invention provides a fuel composition whichis grown and produced using standard agricultural and chemicalprocessing methods. The biodiesel can be converted to a fuel compositionincluding an alkane or a mixture of alkanes.

Biodiesel has various characteristics and properties that make itunattractive for use in cold weather environments and as aviation fuel.For example, biodiesel has an energy density that is lower than requiredfor aviation fuel. Further, at low temperatures, certain moleculeswithin biodiesel begin to agglomerate into solid particles causing thenormally translucent biodiesel to appear cloudy. The highest temperatureat which the biodiesel begins to agglomerate or cloud is called thecloud point. The cloud point is an important characteristic of fuelsused in internal combustion engines and jet engines because the presenceof solid or agglomerated particles causes fuel pumps and injectors toclog rendering the engines inoperable. The cloud point for some commonbiodiesel products are as follows: 0° C. for canola; 1° C. for soybean;−6° C. for safflower; 1° C. for sunflower; −2° C. for rapeseed; 13° C.for jatropha; and 15° C. for palm. The cloud points of various fossilfuels are as follows: 0° C. for ULS diesel; −40° C. for Jet A; −47° C.for JP-8; and −40° C. for ULS kerosene. Aviation fuels have very lowcloud points. For aviation fuels, the low cloud point is importantbecause the fuel must remain liquid at high altitude where temperaturesare well below zero. For ground transportation fuels, a low cloud pointis important because the fuel must remain liquid in cold weatherenvironments where ground vehicles are used.

The cloud point of fuel is a function of its chemical composition. Mostfossil fuels include numerous compounds in the form of linear orbranched chains of carbon atoms with one or more oxygen and hydrogenatoms bound to each carbon atom. For example, a general composition ofconventional aviation fuel is C_(m)H_(n), where _(m) is an integer from12-14, and _(n) is an integer from 20 to 30, and a general compositionof conventional biodiesel is C_(j)H_(k)CO₂CH₃, where _(j) is an integerfrom 14 to 16, and _(k) is an integer from 26 to 33. Jet A and syntheticaviation fuel are both composed of alkanes, which are compounds ofcarbon and hydrogen only. Biodiesel is a vegetable oil or animalfat-based diesel fuel composed of long-chain alkyl esters. Thedifferences between aviation fuels and biodiesel include (i) the size ofthe molecules (biodiesel molecules are larger and include more carbonatoms per molecule) and (ii) the presence of oxygen (biodiesel containsoxygen, whereas aviation fuel is at least substantially oxygen free).

The presence of the oxygen in the biodiesel molecule causes it to have adegree of polarity (an electrostatic charge separation). This polarityresults in an attraction between oxygen in one molecule to hydrogenatoms bound in an adjacent molecule through van der Waal's forces. Thisattractive force among biodiesel molecules causes solidification athigher temperatures than a similar molecule without oxygen. For example,Table 1 shows a comparison of the solidification temperature for variousalkanes, i.e., oxygen-free molecules, and corresponding alcohols, i.e.,oxygen-containing molecules. As shown below, the alcohols have a singleoxygen atom in addition to the corresponding alkane. The alcohol has ahigher solidification point than the corresponding alkane. The presenceof additional oxygen atoms would result in a greater difference insolidification points as compared to the alkane.

TABLE 1 Solidifi- Solidifi- cation cation Alkane Composition (C) AlcoholComposition (C) Methane CH₄ −183 Methanol CH₄O −97 Ethane C₂H₆ −183Ethanol C₂H₆O −115 Propane C₃H₈ −190 Propanol C₃H₈O −127 Butane C₄H₁₀−138 Butanol C₄H₁₀O −90 Hexane C₆H₁₄ −95 Hexanol C₆H₁₄O −47 Octane C₈H₁₈−57 Octanol C₈H₁₈O −16 Dodecane C₁₂H₂₆ −10 Dodecanol C₁₂H₂₆O 24 EicosaneC₂₀H₄₂ 37 Eicosanol C₂₀H₄₂O 66

Thus, it is contemplated by the present invention that the reduction inor removal of oxygen from the biodiesel, i.e., long-chain alkyl esters,will result in a product, i.e., an alkane, having a lower solidificationtemperature or cloud point.

In addition, it is contemplated by the present invention that reducingthe length of the carbon chain in the biodiesel molecule from 16-18carbons to 12-14 carbons will further reduce the solidificationtemperature or the cloud point of the resultant fuel composition.

The reduction or removal of oxygen or oxygen-containing components frombiodiesel can be accomplished by employing a variety of chemical orthermal processes that result in a hydrocarbon, e.g., alkane, havingless or no oxygen. The resulting hydrocarbon (e.g., fuel) will have alower solidification temperature or cloud point than the startingbiodiesel. The process used for the reduction in or removal of oxygenfrom biodiesel can include the reaction of an ester group, e.g., alkylester, with other chemicals either catalytically or electrically. Inaddition to removing oxygen atoms from the ester group, this esterreaction may also remove carbon atoms such that the overall carbon chainlength of the biodiesel molecule is reduced. In one embodiment, the fuelcomposition of the present invention is substantially free of oxygen andhas a carbon chain length of from 12 to 14 carbon atoms. This embodimentproduces a fuel composition that is essentially comparable to aviationfuel (and compatible with aviation fuels to produce a mixture thereof)and can be used as a fuel for ground transportation vehicles in coldclimates. In another embodiment, the produced fuel contains a reducedoxygen content and has a carbon chain length of 12-14 atoms. In afurther embodiment, the fuel composition of the present inventioncontains less than 2000 parts per million of oxygen based on the fuelcomposition.

Biodiesel can be produced by a variety of conventional processes thatare known in the art. Biodiesel is an oil-based diesel fuel, wherein theoil is obtained from a biological source, such as, but not limited to, avegetable oil or animal fat. Oils suitable for use in producingbiodiesel can be oils obtained from a wide variety of biologicalsources. Suitable oils from a biological source can include, but are notlimited to, crop seed oils, vegetables oils, animal oils, animal fats,and combinations thereof. The crop seed oils can be isolated frombiological sources, such as, but not limited to, rapeseed oil, sunfloweroil, mustard oil, canola oil, peanut oil, palm oil, coconut oil, soybeanoil, and mixtures thereof. Additional examples of suitable oils include,but are not limited to, waste vegetable oil; animal fats, includingtallow, lard, yellow grease, chicken fat, by-products of the productionof Omega-3 fatty acids from fish oil, and mixtures thereof; algae; oilfrom halophytes, such as salicornia bigelovii; and mixtures thereof. Inalternative embodiments, the oil from a biological source can bedistilled, separated, or at least partially purified to increase ordecrease the content of a particular component of the oil, such as, butnot limited to, triglycerides, diglycerides, monoglycerides, saturatedfatty acids, unsaturated fatty acids, trilaurin, erucic acid, lauricacid, oleic acid, linoleic acid, linolenic acid, stearic acid, palmiticacid, and mixtures thereof.

In an embodiment, the oil from a biological source can be hydrocrackedin accordance with conventional processes known in the art to yieldsmaller molecular weight species.

Biodiesel includes long-chain alkyl esters, such as, but not limited to,methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester,and mixtures thereof. Biodiesel can be prepared by a transesterificationprocess, wherein lipids are chemically reacted with alcohol. Suitablelipids include the oils derived from biological sources (such as, butnot limited to, vegetable oils and animal fats) described herein.Suitable alcohols include, but are not limited to, ethanol, methanol,propanol, isopropanol, butanol, and mixtures thereof. In addition, thetransesterification process can include the presence of catalyst. Thecatalyst can be selected from a wide variety of materials known in theart to facilitate the reaction between lipids and alcohols. Suitablecatalysts include, but are not limited to, calcium hydroxide, potassiumhydroxide, and mixtures thereof. The transesterification reaction can becarried out using a variety of conventional processes known in the art.Suitable processes include, but are not limited to, common batchprocesses, supercritical processes, and ultrasonic methods. In general,the transesterification reaction converts base oil in the vegetable oranimal starting materials to the desired esters, e.g., alkyl esters, inthe biodiesel product. The transesterification process can produceby-products. For example, free fatty acids present in the base oil aretypically converted to soap and removed from the process or they areesterified using an acidic catalyst. Further, glycerol can be producedas a by-product of the transesterification process. Typically, thiscrude glycerol is purified by employing a conventional purificationprocess known in the art, such as, but not limited to, vacuumdistillation. The refined, purified glycerol then can be utilizeddirectly or converted into other products.

In one embodiment, biodiesel is made by reacting animal fat or vegetableoil with methanol by transesterification. The process yields twoproducts: (i) methyl esters, i.e., biodiesel, and (ii) glycerin, i.e., aby-product that can be used for the production of soap. In alternateembodiments, this process can be conducted on any scale, e.g., in amason jar or in a large-scale production facility.

In another embodiment, vegetable oil or animal fat reacts with ethanolor methanol or mixtures thereof, and a catalyst, such as calciumhydroxide or potassium hydroxide or a mixture thereof. In a furtherembodiment, the initial oil or fat is relatively low in free fatty acidsin order to reduce or prevent the formation of soap. The reactants aremixed thoroughly for about an hour at room temperature orslightly-elevated temperature. In one embodiment, the temperature isfrom about 20° C. to about 50° C. After about one hour of mixing, thesolution is allowed to settle.

During the settling time, the heavy glycerin (glycerol) settles to thebottom of the solution and biodiesel is formed on top. The glycerin isthen separated by, for example, draining it from the bottom of asettling tank. In an alternate embodiment, separation can beaccomplished by using a centrifuge which is typically employed in largescale production of biodiesel to reduce the time needed to carry out theprocess.

The final steps in the process include washing and drying the biodieselusing conventional methods known in the art. In one embodiment, a finemist of water is applied to the biodiesel to absorb any trace amounts ofthe catalyst remaining in the biodiesel. This is separated from thebiodiesel, for example, in the same manner as the glycerin separation. Asubsequent bubbling of air through the biodiesel removes any remainingwater to ensure a high purity biodiesel product for use in dieselengines.

In another embodiment, wherein the starting material contains asignificant amount of free fatty acids (as is typical in vegetable oilafter it is used for cooking or animal fat), a pretreatment of the freefatty acid can be conducted using conventional methods known in the art.For example, the vegetable oil or animal fat can be reacted withhydrochloric acid and methanol. This pretreatment converts the freefatty acids into biodiesel. After washing and drying the hydrochloricacid from the resulting solution using a conventional method known inthe art, the remaining vegetable oil can be converted to biodiesel usingthe transesterification process described herein.

The following table gives approximate amounts of the reactants needed toproduce one gallon of biodiesel in accordance with an embodiment of theinvention. The amounts can depend on the level of free fatty acid andwater in the feedstock vegetable oil or animal fat.

TABLE 2 Feedstock (veg. oil or animal fat) 1 gal Methanol 0.1667 galPotassium hydroxide 0.0435 kg Hydrochloric Acid 0.001 Gal Water 0.4 GalElectric Power 0.6667 kW/Gal/hr

In one embodiment of the present invention, multiple reactions may benecessary to reduce or remove the oxygen and/or oxygen-containingcompounds from biodiesel to produce a fuel having a low solidificationtemperature or cloud point for use in cold climates or as aviation fuel.For example, an ester, such as an alkyl ester in biodiesel, can bereduced to two alcohols through a reaction with lithium aluminum hydride(LiA1H₄). This nucleophilic acyl substitution reaction is generallyconducted as follows:

FIG. 1 shows a four-step reaction process for reducing an ethyl ester(I) to ethanol (V). In FIG. 1, the nucleophilic hydrogen atom (H) fromthe hydride reagent (LiA1H₄) adds to the electrophilic carbon (C) in thepolar carbonyl group of the ester (I). Electrons from the carbon andoxygen double bond (C═O) move to the electronegative oxygen atom (O)creating an intermediate metal alkoxide complex (II).

The tetrahedral intermediate collapses and displaces the alcohol portionof the ester as a leaving group, which produces a ketone as anintermediate (III).

The nucleophilic H from the hydride reagent adds to the electrophilic Cin the polar carbonyl group of the aldehyde. Electrons from the C═O moveto the electronegative O creating an intermediate metal alkoxide complex(IV).

The final step is a simple acid/base reaction. Protonation (H+) of thealkoxide oxygen creates the primary alcohol product (V) from theintermediate complex.

Reduction of the resultant alcohol to alkane can be accomplished by avariety of chemical processes. FIG. 2 shows a process forchemoselectively reducing secondary and tertiary alcohols to alkanes.This direct pathway shows selective reduction of the hydroxyl (OH)moiety without affecting other functional groups. In FIG. 2, 2-decanol(compound 1a) is reduced to decane (compound 2a) using this process. Thereducing system in FIG. 2 includes dissolving 2-decanol in a CH₂ClCH₂Clsolvent with hydrosilane and indium chloride (InCl₃) catalyst, at atemperature of about 80° C. for about 4 hours.

The fuel composition of the present invention can provide at least oneof the following benefits:

-   -   Reduced solidification temperature or cloud point; and    -   Agricultural-based starting materials.

In one embodiment, wherein the fuel composition of the present inventionincludes the conversion of biodiesel fuel to ground transportation fuelor aviation fuel, the cloud point of the fuel composition is less thanthe cloud point of the biodiesel. In another embodiment, wherein thefuel composition of the present invention is used as aviation fuel, thecloud point can be less than or equal to about −40° C. In anotherembodiment, wherein the fuel composition of the present invention isused as ground transportation fuel in cold temperature conditions, thecloud point can be less than about −20° C. Cold climate conditions canvary and in one embodiment, cold climate temperatures can be less thanor equal to about 0° C.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention, which is to be given thebreadth of the appended claims and any and all equivalents thereof.

1. A fuel composition, comprising: oil derived from a biological source;and alcohol, wherein the fuel composition is at least substantially freeof oxygen and oxygen-containing compounds.
 2. The fuel composition ofclaim 1, where the oil is selected from the group of biological sourcesconsisting of vegetable oil, crop seed oil, animal oil, animal fat andcombinations thereof.
 3. The fuel composition of claim 1, wherein thealcohol is selected from the group consisting of methanol, ethanol,propanol, isopropanol, butanol and mixtures thereof.
 4. The fuelcomposition of claim 1, wherein the fuel composition is oxygen-free. 5.The fuel composition of claim 1, wherein the fuel composition has alevel of oxygen that is less than the level of oxygen in biodiesel. 6.The fuel composition of claim 1, wherein the fuel composition has alevel of oxygen that is less than 2000 parts per million oxygen based onthe fuel composition.
 7. The fuel composition of claim 1, wherein thefuel composition includes molecules and each of the molecules has acarbon chain length of from 12 to 14 carbons atoms.
 8. The fuelcomposition of claim 1, wherein the fuel composition is used foraviation fuel.
 9. The fuel composition of claim 1, wherein the fuelcomposition is used for ground transportation fuel in a cold climate.10. The fuel composition of claim 1, wherein the fuel compositioncomprises an alkane.
 11. The fuel composition of claim 1, wherein thefuel composition further comprises catalyst.
 12. The fuel composition ofclaim 11, wherein the catalyst is selected from the group consisting ofcalcium hydroxide, potassium hydroxide and mixtures thereof.
 13. Amethod for preparing a fuel composition, the method comprising: reactingoil derived from a biological source and alcohol to produce an alkylester-containing product, removing at least a portion of oxygen from thealkyl ester-containing product to produce a fuel composition which is atleast substantially free of oxygen and oxygen-containing compounds. 14.The method of claim 13, wherein the alkyl ester-containing productcomprises alkyl ester selected from the group consisting of methylester, ethyl ester, propyl ester, isopropyl ester, butyl ester andmixtures thereof.
 15. The method of claim 13, wherein the alkylester-containing product comprises biodiesel.
 16. The method of claim13, wherein the reacting step is conducted in accordance with atransesterification reaction.
 17. The method of claim 13, wherein theremoving step is conducted in accordance with a nucleophilic acylreaction.
 18. The method of claim 13, wherein the cloud point of thefuel composition is lower than the cloud point of the alkylester-containing product.
 19. The method of claim 13, wherein theremoving step further comprises removing a portion of carbon atoms fromthe alkyl ester-containing product.
 20. The method of claim 13, whereinthe fuel composition comprises molecules and each of the molecules has acarbon chain length of from 12 to 14 carbon atoms.